Telescopic strut for an external fixator

ABSTRACT

A telescopic strut for use with an external fixator comprising an axially extending rod; an axially extending tube moveably recurring the rod for varying the length of the rod and tube combination along a longitudinal axis; the tube having first and second ends, the second end having a pin extending therethrough; a locking system mounted on the tube first end for adjusting the position of the rod in the tube and fixing the length of the rod and tube combination; a coupling element having a tubular sleeve with a threaded outer surface mounted on an outer surface of the second end of the tube, the sleeve having two diametrically opposed slots receiving the pin and an adjustment element threadably mounted on the sleeve outer surface for axial movement along the axis, the adjustment element having a surface contacting the pin to limit the movement of the pin in the slots.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/549,949, filed on Nov. 21, 2014, which is a continuation of U.S.patent application Ser. No. 13/589,624 filed on Aug. 20, 2012 and issuedas U.S. Pat. No. 8,906,021, the disclosures of which are both herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to a telescopic strut for an external fixator,especially for use with an external ring fixator.

A plurality of compression-distraction apparatus have been designed andimproved by Ilizarov and his group using two external rings to be placedaround the limb to be fixed. There are usually at least two such rings,one proximal and one distal ring, which are connected with a pluralityof struts or rods. Preferably, these struts are linked to the rings in away that the attachment points can be pivoted and the length of thestrut can be varied to enable adjustment of the external fixation rings.

Ilizarov has also provided some improvements for said systems. EuropeanPatent No. 0 377 744 shows a telescopic strut for such an externalfixator. U.S. Pat. No. 4,615,338 shows a further device to control thelength of such telescopic struts.

A different external ring fixator having telescopic struts is shown inU.S. Pat. Nos. 5,702,389 and 6,030,386. Other telescopic struts areshown in U.S. Pat. Nos. 8,057,474 and 8,062,293 assigned to the assigneeof the present invention, the disclosures of which are incorporatedherein by reference.

BRIEF SUMMARY OF THE INVENTION

However, these devices, which can be used to shorten or lengthen thetelescopic struts, are difficult to adjust and it is one aspect of theinvention to improve the ease of adjusting the length of the rod.Furthermore, a simple method of length adjustment and dynamization foreach strut is desired.

Based on the prior art, it is therefore an aspect of the invention toprovide a telescopic strut, which can be readily and quickly changed inits length.

It is another aspect of the invention, to allow, as an alternative, fineadjustments of the struts.

In view of the above mentioned aspect it is furthermore another aspectof the invention to allow a quick switch between the two functions,i.e., to allow a quick first definition of the length of the telescopicelement, and additionally, to switch for a fine adjustment of saidlength.

It is yet another aspect to provide a variable dynamization function tothe strut which allows micro-motion at a fracture/fusion site to promotehealing.

A telescopic strut of the present invention for use with an externalfixator includes an axially extending rod having a series ofcircumferential grooves on an outer surface of the rod; an axiallyextending tube is provided for receiving the rod. The tube has a firstend including a plurality of holes formed in a wall of the tube and asecond end having a pin extending therethrough. A plurality of balls areprovided for extending through the holes in the first end of the tube. Asleeve having an eccentric bore therethrough is mounted around the tubefirst end for contacting the balls. The eccentric bore has a majordiameter allowing the balls to be located outside the grooves of the rodand a minor diameter causing the balls to be held within the grooves onthe rod. A coupling element comprising a hollow tubular member isslidably mounted on an outer surface of the tube second end, thecoupling element tubular member has two axially extending diametricallyopposed slots for receiving the pin and an adjustment element is mountedon an outer surface of the coupling element tubular member for movementthereon in the axial direction. The adjustment member serves as a stopto limit the travel of the pin in the two slots. The adjustment membermay be threaded and mounted on a mating thread on the coupling elementtubular member.

A detent may be provided for holding the sleeve in a first positionwhere the major diameter engages the balls or a second position wherethe minor diameter engages the balls. The means includes a springbiasing the sleeve towards the second position.

The grooves in the rod may be formed by a helical thread extending alongthe axial extent thereof so that rotation of the rod with the ballsengaged lengthens the strut.

Alternately the grooves may be formed by a plurality of radial ridges.

Preferably the balls are at least partially retained within the holes ofthe leading end when contacted by the minor diameter of the sleeve.

A telescopic strut of the present invention for use with an externalfixator may also comprise an axially extending rod, an axially extendingtube moveably receiving the rod for varying the length of the rod andtube combination along a longitudinal axis. The tube has first andsecond ends, the second end having a pin extending therethrough. Anadjustment system is mounted on the tube first end for adjusting theposition of the rod in the tube. A connector element is provided havinga tubular sleeve with a threaded outer surface mounted on an outersurface of the second end of the tube. The connector element can includea ball joint which can be locked when the connector is fixed in a holein a ring of an external fixation frame. The sleeve has two axiallyextending diametrically opposed slots for receiving the pin and anadjustment element threadably mounted on a threaded portion of thetubular sleeve outer surface for axial movement along the axis. Theadjustment element has an annular surface contacting the pin to limitthe movement of the pin in the slots.

The rod is threaded and is mounted in the end of the tube such thatrelative rotation therebetween causes a length variation of the rod andtube combination along the longitudinal axis.

The adjustment system may include radially moveable elements whichselectively engage and disengage the threaded rod to allow axial slidingwhen disengaged and fine adjustment by the relative rotation of the tubeand rod when engaged to vary the strut length.

The tubular sleeve is coupled to an opening in an external fixation ringby releasable connectors which allow rotation of the sleeve and tubeabout the axis of the rod and tube to vary the axial length of rod andtube when the radially moveable elements are engaged.

The two slots in the connector sleeve each have a first end and theadjustment element can move the pin into contact with the slot first endto prevent the pin from moving in the two slots. The sleeve outersurface includes markings showing the distance between the slot firstend and the pin wherein the markings are in 1 mm increments.

The pin may include a pair of protruding ends for receiving a tool forrotating the tubular sleeve and tube relative to the rod for varying thelength of the strut.

An additional telescoping strut of the present invention for an externalfixator comprises a threaded rod, a tube threadably receiving the rodwith the tube and rod extending along a longitudinal axis. The tube hasa first end with a pin extending therethrough. An adjustment element isprovided for fixing the relative axial position of the tube and rod; anda dynamization system mounted on the first end of the tube, the systemcomprising a sleeve slidably mounted on the tube with the pin extendingthrough a pair of diametrically opposed slots on the sleeve such thatthe pin can move in the axial direction with respect to the slots; anadjustable stop element mounted on the sleeve movable to limit the levelof the pin in the slots. The adjustable stop element is a nut mounted ona threaded outer surface of the sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described with reference to the enclosed drawings,showing preferred embodiments of the telescopic strut:

FIG. 1 is an elevation view of a telescopic strut according to theinvention;

FIG. 2 is an exploded view of the length adjusting portion of thetelescopic strut according to FIG. 1;

FIG. 3 is a side view in cross-section of the telescopic strut accordingto FIG. 1;

FIG. 4 is a cross section of the rod along line-4 in FIG. 3;

FIG. 5 is an elevation view of the coupling element connected to thethreaded rod of the strut for coupling the strut to a ring of anexternal fixation system;

FIG. 6 is a cross-sectional view of the connector of FIG. 5;

FIG. 7 is an elevation view of a coupling element connected to thetubular portion of the strut of the present invention for connecting thestrut to a second ring element of an external fixation system;

FIG. 8 is a cross-sectional view of the connection element of FIG. 7;

FIG. 9 shows an adjustment wrench for adjusting the dynamization of thestrut of the present invention;

FIG. 10 shows the same adjustment wrench adjusting the length of thestrut of the present invention; and

FIG. 11 is an isometric view of the wrench shown in FIGS. 9 and 10.

DETAILED DESCRIPTION

Referring to FIG. 1 there is shown a perspective view of a telescopicstrut according to the invention generally denoted as 10. The telescopicstrut comprises two free ends 11 and 12, which include coupling elements100 and 200 being attachment points for connecting the strut to twoexternal rings to be placed around the limb to be treated. Theattachment coupling elements 100 and 200 according to this embodimentpreferably comprise ball joints as will be discussed below, but thisentirely depends on the kind of fixation element for which the rod isused.

FIG. 1 shows the main components of the telescopic strut. There is anouter tube tubular element 21 having a bore in which the threaded rod 22is partially located. Tube 21 has a bore therein for receiving rod 22the bore can be only partially through tubular element 21 leaving asolid end adjacent coupling 200. The outer tube 21 has mating threadelements 30 for engaging threaded rod 222 which is located within asleeve 23 at an end of tubular element 21 and are better seen in FIG. 2as well as FIG. 3 and will be described below. In the preferredembodiment sleeve 23 comprises a bayonet groove 24 for a quick changebetween the desired quick length change mode and the fine adjustmentmode. The sleeve 23 can be switched between two rotational positions forthis, i.e., to lock and unlock movement the axial direction. Thereforethe groove 24 has a U-form, the ends of the groove 24 defining the twopositions with the help of a bolt 26 provided within the groove 24. Therecessed ends 24 a and 24 b of the groove 24 are oriented in axialdirection of the telescopic strut. These ends face in the samedirection, towards the spring 27, as can be seen in FIG. 1 and theexploded view of FIG. 2, to allow displacement of the bolt 26 againstthe force of spring 27.

A security mechanism, to avoid unintentional switching, is realized byan additional nut 25, blocking the bolt 26 in one of the free ends ofgroove 24.

FIG. 3 shows a view in cross-section of the telescopic strut accordingto FIG. 1. Sleeve 23 can be pushed against action of spring 27 providedon the outer tube 21 and which spring is biased with help of nut 25.Then the sleeve 23 is turned around 90° and is arrested within the otherfree end 24 a or 24 b of the groove 24. It is preferred that thisposition is fixed through nut 25.

The turning angle of 90 degrees is defined in view of the way the quicklength adjustment mode is working. This can be seen in FIG. 4 being arepresentation of a cross section of the rod along line 4-4 in FIG. 3.It can be seen from FIG. 4 that the sleeve 23 has a non-cylindricalinner bore. The bore can be, e.g., elliptical. The shorter diameter ofthe bore is sufficient to accommodate the outer diameter of the foremostportion 25 a of outer tube 21 shown in FIG. 2, which is cylindrical.Foremost portion 25 a comprises on both sides a plurality of preferably,four holes 38 to accommodate one ball 28 each. Of course, it is alsopossible to provide only two balls on each side or five or more. Threeor four balls have been proven to be sufficient without lengthening thesleeve 23 too much.

The inner diameter of outer tube 21 is greater than the outer threadportion of the rod 22 which is cylindrical. Therefore, the rod 22 can bepushed into the outer tube 21, when the bolt 26 is in a position whichallows the sleeve 32 to be oriented as shown in FIG. 4. Then the balls28 can freely move against the inner wall of sleeve 23 and the rod 22can be axially pushed. For that the sum of the outer diameter of the rod22 and twice the diameter of the balls 28 is less or nearly equal to theinner diameter of the sleeve 23.

Separation of the threaded rod 22 from the outer tube 21 is preventedthrough an abutment screw 29 which is screwed into a correspondingthread within the threaded rod 22 and which can abut on a correspondingshoulder within the tube 21 as shown in FIG. 3

By turning the sleeve 23 around the bolt 26, i.e., by 90°, the balls 28will be moved because of the elliptic inner shape within the sleeve 23.In this way the balls 28 are pushed through holes 38 towards the groovesof the thread 22 for interlocking, i.e., connecting the thread with theouter tube 21, because the balls 28 stand within both parts and leave noroom to allow a direct axial movement of the threaded rod 22.

In this position the threaded rod 22 still can be moved axially throughrotational movement of tube 21 being directly coupled via bolt 26 tosleeve 23 against the threaded rod 22 which can rotate in view of theballs 28 pressed in its threads. This allows for the fine adjustment.

Thus the elements allow for a quick change between free axial adjustmentof the telescopic strut, if the balls 28 do not engage the threaded rod22. If the balls do engage rod 22 then a fine adjustment throughrotation of the outer tube 21/rod 22 is allowed. The balls 28 areengaging the one or subsequent grooves of the threaded rod 22, e.g.,depending on the pitch of thread of the rod 22. The pitch angle of thethread can be chosen, e.g., between 30 and 60 degrees and especiallybetween 40 and 50 degrees.

It is clear that this fine adjustment is only possible, if at least onefree end 11 or 12 of the telescopic strut can be rotated while fixedwithin an external fixator ring.

Within another embodiment (not shown) a helically threaded rod isreplaced by a rod having a plurality of radial grooves. Each of thesegrooves has dimensions to accommodate one of the balls 28. In otherwords, the threaded rod having a groove providing a pitch is replaced bya sequence of separated adjacent radial grooves. It is thus possible touse such a rod with a flank lead to block the device in a plurality ofpositions. However, with radial grooves it is not possible to allow afine tuning through rotation of tube 21.

Referring to FIGS. 5 and 6, there is shown a first coupling elementadapted to engage a bore in a ring of an external fixation system.Typically the rings of an external fixation system are circular or partcircular and have a plurality of through holes located between inner andouter diameters of the rings. FIGS. 5 and 6 show first coupling element100, including a shaft 102 with a threaded portion 104 and a pivotingtubular end portion 106 adapted to thread on an end of rod 22 of strut10. As can be seen in cross-sectional view FIG. 6, the inner bore 108 ofend 106 includes threads 110 adapted to be screwed onto the end of rod22. Pivot end 106 includes an end portion 112 having an outerpart-spherical surface 114 and an inner part spherical surface 116.Outer part-spherical surface 114 may include roughened areas or ridges118 so that it may be locked against a part spherical recess 120 onshaft portion 102 when the assembly is tightened. Pivot portion 106 iscoupled to shaft portion 102 via a threaded nut 122 having a partspherical surface 124 adapted to engage inner part spherical surface 116of pivot end 106. Nut 122 includes a threaded inner bore diameter 126.Nut 122 also includes a generally cylindrical leading end 128, whichslidably engages a bore 130 within shaft 102. Shaft 102 includes afurther bore portion 132 for receiving a screw 134, which bore has asmaller diameter than bore portion 130 so that leading end 128 of nutportion 122 may slidably engage the larger diameter bore 130 and stillreceive a threaded shaft 133 of a screw or tightening element 134mounted in bore portion 132. Bore portions 130, 132 and shaft 133 extendalong an axis 140. Screw element 134 may be threaded into the threadedbore 126 of nut 122 via an outer threaded portion 136 thereon.Tightening element 134 includes a drive head 138, which may be square orhexagonal so that a tool may be applied to rotate element 134 therebymoving surface 124 of nut 122 into tight engagement with inner surface116 of pivot end 106. Portion 112 of pivot element 106 may have two ormore longitudinal slits therein so that it may flex outwardly intoengagement with part-spherical surface 120 upon movement of nut 122toward surface 116 resulting from rotation of threaded tighteningelement or screw 134.

In use threaded portion 104 of coupling 100 is inserted through a holein the external fixation system ring (not shown) and a nut is threadedonto thread 104 of shaft 102 to attach coupling element 100 to the ring.When this is done axis 140 of end 102 is co-axial with a central axis ofthe bore in the ring. When the end of rod 22 is threaded into pivot end106, it can be selectively locked in position or rotated about the balljoint in any direction about axis 140 of coupling 100 on part-sphericalsurfaces 114 and 120 depending on whether screw element 134 and nut 122are either in a loosened position or a tightened down position. Whentightened roughened surface 118 engages inner surface 116 which ensuresno movement of rod 22 with respect to the axis 140 of the hole in thering and of portion 102.

Referring to FIGS. 7 and 8, a second coupling element 200 is shown.Coupling element 200 includes many of the features of coupling 100,including a shaft 102 a with a threaded portion 104 a. Likewise, a screw134 a with drive head 138 a is coupled to a nut 122 a having the partspherical outer surface 124 a. Also likewise, the coupling element 200includes a pivoting tubular end portion 106 a extending along an axis203, which has a leading end 112 a with part spherical surface 114 a forcontacting an inner surface 120 a of element 102 a. Tubular end 106 a isslidably mounted on end 21 a of shaft 21. End portion 106 a includes ahollow end portion 108 a fixedly receiving shaft 21 or an extensionthereof such that pivot end portion 106 a and shaft 21 cannot rotaterelative to one another. Portion 106 a now includes a threaded outerportion 202 upon which a rotatable internally threaded nut 204 ismounted. Rotation of nut 204 on threaded portion 202 moves the nut 204along axis 203 either away from or toward end 108 a and shaft 21. AnO-ring 206 is mounted in a groove 208 within nut 204 to hold nut 204 ina particular axial location upon rotation of nut 204 on threaded portion202. Tubular element 106 a further includes a pair of slots 210diametrically opposite one another in a wall of tubular element 106 a.Shaft portion 21 includes a pin 212 extending therethrough which pin 212is fixed to the end of shaft 21 such as by a press fit. Upon assembly,pin 212 extends through both slots 210 in 106 a and extends outwardlybeyond the outer surface on each side of tubular member 106 a, adistance preferably approximately equal to the diameter of nut 204.Since tubular end portion 106 a is slidable on end 21 a of shaft 21 theengagement of slot 210 and pin 212 hold the tubular end portion 106 a onend 21 a. As will be discussed below, the engagement of end surface 214of nut 204 with pin 212 as it moves within slot 210, provides fordynamization within the strut 10 by allowing the surgeon to set adynamization distance of, for example, 0 mm to 5 mm by rotation of nut204. This distance would be set by rotating nut 204 on thread 202.Typically, 1 mm spaced markings placed on the outer surface of tubularelement 106 a would indicate the distance.

In use, the telescopic strut would be used as described above and inU.S. Pat. No. 8,057,474, the teachings of which are hereby incorporatedby reference, with the exception of the dynamization system discussedabove. The surgeon connects strut 10 with coupling elements 100 and 200to respective first and second external fixation frame members such asrings or plates with the threadable elements 134, 134 a loosened so thatthe part-spherical ball joints are free to rotate. The surgeon adjuststhe length of the strut initially using the quick length adjustment modeand then the fine adjustment mode until the fractured bones are in thedesired alignment. At this point, the screws 134, 134 a are bothtightened thereby locking the strut in the desired angular and lengthposition with respect to both the first and second ring members. Afurther finer adjustment is needed then one of the ball joints must beloosened by rotating a screw 134 a which allows for rotating the tubularshaft 21 or rod 22. Preferably the ball joint 200 is loosened byrotating screw 134 a. The surgeon then sets the dynamization system byrotating nut 204. If no dynamization is required surface 214 of nut 204is placed against pin 212. Obviously multiple struts 10 may be used inthe frame system.

Referring to FIGS. 9-11, there is shown the use of a wrench 300 used toboth make the fine adjustments of the length of strut 10, as well as setthe dynamization distance between pin 212 and surface 214 of nut 204.Wrench 300 includes a first end 302 with a curved opening 304 definingfirst lobe 306, second lobe 308, and third lobe 310 adapted torespectively engage one of a plurality of grooves 215 on the outside ofnut 204. As seen in FIG. 9, lobes 306, 308, and 310 engage threedifferent grooves 215. Thus rotation of wrench 300 can move nut 204 onthread 202 either toward or away from pin 212. Tubular member 106 aincludes a series of markings 217 either cut or etched into the outersurface of tubular element 106 a at 1 mm increments. Thus, the surgeoncan set the dynamization by turning nut 204 thereby moving surface 214with respect to pin 212. Preferably markings 217 are spaced 1 mm so thatthe exact amount of dynamization can be determined by counting thenumber of markings 217 between surface 214 and the under surface of pin212.

Wrench 300 has a second end 320 with a pair of hook shaped elements 322and 324, which each include a U-shaped recessed opening 326, whichreceives the ends of pin 212 which extend beyond the outer surface oftubular element 106 s. As shown in FIG. 10, when end 320 is hooked overboth ends of pin 212, wrench 320 can be used to rotate shaft 21. End 21a is slidably mounted within tubular element 106 a however rotation ofend 21 a via pin 212 rotates tubular portion 106 a via the engagement ofpin 212 and slot 210 thus providing fine tuning of the length of strut10. As discussed above, in order to accomplish this, the ball jointwithin coupling element 200 must be released by appropriately turningscrew 134 a. Once the correct length is achieved, the ball joint isagain locked via rotation of screw 134 a. Locking end 112 a of sleeve106 a against surface 120 a via threaded element 134 a prevents rotationof shaft 21 about any axis

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. (canceled)
 2. A system for adjusting a relative orientation of a pairof spaced rings of an external fixator, comprising; a rod extendingbetween a first end and a second end along a first axis; a tubularelement extending between a first end and a second end along the firstaxis, the first end of the tubular element for receiving the first endof the rod; a first coupling element attached to the second end of therod for coupling the rod to one of the pair of spaced rings, the firstcoupling element comprising: a tube having a first end and a second endopposite the first end, the first end of the tube being fixed to thesecond end of the rod, the second end of the tube having an outerpart-spherical surface and an inner part-spherical recess; a shaftextending from a first end to a second end, the second end of the shafthaving a part-spherical recess that at least partially overlies and isin contact with the outer part-spherical surface of the tube; and a nutextending from a first end to a second end, the first end of the nutbeing positioned within the second end of the tube and having an outerpart-spherical surface in contact with the part-spherical recess of thetube, the second end of the nut being positioned within the second endof the shaft, the shaft and the nut each being articulable with respectto the tube; and a second coupling element attached to the second end ofthe tubular element for coupling the tubular element to the other of thepair of spaced rings.
 3. The system of claim 2, wherein the outerpart-spherical surface of the tube includes a roughened area.
 4. Thesystem of claim 3, wherein the roughened area includes ridges.
 5. Thesystem of claim 2, wherein the first coupling further includes atightening element extending at least partially through a bore in theshaft and a bore in the nut.
 6. The system of claim 5, wherein the firstcoupling element has a loosened condition in which the shaft and the nutare each articulable with respect to the tube, and a tightened conditionin which the shaft and the nut are locked from articulating with respectto the tube.
 7. The system of claim 6, wherein in the loosened conditionof the first coupling element, the nut has a first position relative tothe tightening element, and in the tightened condition of the firstcoupling element, the nut has a second position relative to thetightening element, actuation of the tightening element sliding the nutfrom the first position to the second position.
 8. The system of claim7, wherein the tightening element is a screw having outer threadscoupled to inner threads of the nut.
 9. The system of claim 7, whereinthe second end of the tube includes at least two longitudinal slitstherein.
 10. The system of claim 9, wherein the second end of the tubeis in a flexed condition when the first coupling element is in thetightened condition, and in an unflexed condition when the firstcoupling element is in the loosened condition.
 11. The system of claim6, wherein the bore of the shaft includes a first bore portion in thefirst end of the shaft having a first diameter and a second bore portionin the second end of the shaft having a second diameter larger than thefirst diameter, the first bore portion being continuous with the secondbore portion.
 12. The system of claim 11, wherein the tightening elementextends through the first and second bore portions of the shaft.
 13. Thesystem of claim 12, wherein the second end of the nut has an outerdiameter that is smaller than the second diameter of the second boreportion and larger than the first diameter of the first bore portion.14. The system of claim 11, wherein the first bore portion, the secondbore portion, and the shaft each extend along a second axis.
 15. Thesystem of claim 14, wherein in the loosened condition of the firstcoupling element, the first axis is moveable with respect to the secondaxis, and in the tightened condition of the first coupling element, thefirst axis is fixed with respect to the second axis.
 16. The system ofclaim 2, wherein the second coupling element comprises: a second tubehaving a first end and a second end opposite the first end, the firstend of the second tube being fixed to the second end of the tubularelement, the second end of the second tube having an outerpart-spherical surface and an inner part-spherical recess; a secondshaft extending from a first end to a second end, the second end of thesecond shaft having a part-spherical recess that at least partiallyoverlies and is in contact with the outer part-spherical surface of thesecond tube; and a second nut extending from a first end to a secondend, the first end of the second nut being positioned within the secondend of the second tube and having an outer part-spherical surface incontact with the part-spherical recess of the second tube, the secondend of the second nut being positioned within the second end of thesecond shaft, the second shaft and the second nut each being articulablewith respect to the second tube.